1. Field of the Invention
This invention relates generally to wireless communication systems and more particularly to supporting multiple wireless communication protocols within a wireless local area network by formatting, modulating, and coding a signal.
2. Description of the Related Art
Wireless and wire lined communications between wireless or wire lined communication devices use networks and systems to exchange information and data. Communication systems may include national or international cellular telephone systems to the Internet to point-to-point in-home wireless networks. Each type of communication system may operate in accordance with one or more communication protocol standards. For example, wireless communication systems may operate in accordance with one or more protocol standards including, but not limited to, IEEE 802.11, Bluetooth, advanced mobile phone services (AMPS), digital AMPS, global system for mobile communications (GSM), code division multiple access (CDMA), local multi-point distribution systems (LMDS), multi-channel-multi-point distribution systems (MMDS), and the like. The applicable protocol for wireless communications standard may vary. As the IEEE 802.11 specification has evolved from IEEE 802.11 to IEEE 802.11b (standard 11b) to IEEE 802.11a (standard 11a) and to IEEE 802.11 g (standard 11 g), wireless communication devices that are compliant with standard 11b may exist in the same wireless local area network (WLAN) as standard 11g compliant wireless communication devices.
When legacy devices such as those compliant with an earlier version of a standard reside in the same WLAN as devices compliant with later versions of the standard, mechanisms or processes may be employed for the legacy devices to know when the newer version devices are utilizing the wireless channel to avoid interference or a collision. A legacy system may be an existing system that is in place and available for use in wireless local area networks. The issue of legacy systems may be important because these systems may remain in place after new standards, methods or networks for future wire local area networks are implemented.
The different protocols or standards may operate within different frequency ranges, such as 5 to 6 gigahertz (GHz) or, alternatively, 2.4 GHz. For example, standard 11a may operate within the higher frequency range. An aspect of standard 11a is that portions of the spectrum, between 5 to 6 GHz, are allocated to a channel for wireless communications. The channel may be 20 megahertz (MHz) wide within the frequency band. Standard 11a also may use orthogonal frequency division multiplexing (OFDM). OFDM may be implemented over subcarriers that represent lines, or values, within the frequency domain of the 20 MHz channels. A signal may be transmitted over different subcarriers within the channel. The subcarriers may be orthogonal to each other so that information or data is extracted off each subcarrier about the signal.
Backward compatibility with legacy devices may be enabled at the physical (PHY) layer or the Media-Specific Access Control (MAC) layer. At the PHY layer, backward compatibility is achieved by re-using the PHY preamble from a previous standard. Legacy devices may decode the preamble portion of all signals, which provides sufficient information for determining that the wireless channel is in use for a specific period of time, to avoid interference and collisions even though the legacy devices cannot fully demodulate or decode the transmitted frame(s).
At the MAC layer, backward compatibility with legacy devices may be enabled by forcing devices that are compliant with a newer version of the standard to transmit special frames using modes or data rates that are employed by legacy devices. These special frames may contain information that sets the network allocation vector (NAV) of legacy devices such that these devices know when the wireless channel is in use by newer stations.
As new standards or protocols are implemented, backward compatibility of receiving and transmitting signals may become more of a concern. New signaling formats may desire more robustness than legacy formats. Further, frames exchanged within a wireless system may include immediate acknowledgement capabilities, bursting information and exchanging more bits of information than frames used by legacy devices.